In a liquid crystal display device, a classification based on an operating mode for liquid crystal molecules includes a phase change (PC) mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, an electrically controlled birefringence (ECB) mode, an optically compensated bend (OCB) mode, an in-plane switching (IPS) mode, a vertical alignment (VA) mode, a fringe field switching (FFS) mode and a field-induced photo-reactive alignment (FPA) mode. A classification based on a driving mode in the device includes a passive matrix (PM) and an active matrix (AM). The PM is classified into static, multiplex and so forth, and the AM is classified into a thin film transistor (TFT), a metal insulator metal (MIM) and so forth.
The device is sealed with a liquid crystal composition. Physical properties of the composition relate to characteristics in the device. Specific examples of the physical properties in the composition include stability to heat or light, a temperature range of a nematic phase, viscosity, optical anisotropy, dielectric anisotropy, specific resistance and an elastic constant. The composition is prepared by mixing many liquid crystal compounds. Physical properties required for a compound include high stability to environment such as water, air, heat and light, a wide temperature range of a liquid crystal phase, small viscosity, large optical anisotropy, large dielectric anisotropy, a suitable elastic constant and good compatibility with other liquid crystal compounds. A compound having high maximum temperature of the nematic phase is preferred. A compound having low minimum temperature in the liquid crystal phase such as the nematic phase and a smectic phase is preferred. A compound having the small viscosity can shorten a response time in the device. A compound having large optical anisotropy can decrease cell thickness in the device, and therefore can shorten the response time. A compound having large positive or negative dielectric anisotropy is preferred for driving the device at low voltage. A compound having good compatibility with other liquid crystal compounds is preferred for preparing the composition. The device may be occasionally used at a temperature below freezing point, and therefore a compound having good compatibility at low temperature is preferred.
Many liquid crystal compounds have been so far prepared. Development of a new liquid crystal compound has been still continued. The reason is that good physical properties that are not found in conventional compounds are expected from a new compound. The reason is that the new compound may be occasionally provided with a suitable balance regarding at least two physical properties in the composition. Only a limited number of reports has been found on a compound having a biphenylene ring.
JP H10-236993 A describes liquid crystal compounds (S-1) and (S-2) having a 1,8-difluorobiphenylene-3,7-diyl group.
